Optical film comprising polyarylates containing bis-(hydroxyphenyl)-fluorene-ortho-disubstituted bisphenols

ABSTRACT

The present invention refers to an optical film comprising one or more polyarylates having at least some units represented by the general structure:  
                 
 
     wherein A represents one or more different bisphenolfluorene radicals having the general formula (I):  
                 
 
     wherein R 1  and R 2  independently represent an alkyl group, a halogen, an alkoxy group, an acyl group, a phenyl group or a nitrile group, with the proviso that R 1  and R 2  are not both an alkyl group; R 3 , R 4 , R 5  and R 6  represent a hydrogen atom, an alkyl group, a halogen, an alkoxy group, an acyl group, a phenyl group, a nitro group, or a nitrile group;  
     B represents one or more different dicarboxy radicals having the formula:  
                 
 
     wherein X is a divalent hydrocarbon group having from 1 to 20 carbon atoms, and n is the number of the repeating units which build up the polymer and is a positive integer higher than 20.  
     The optical film of the present invention has excellent mechanical and thermal properties, a high Tg and does not readily yellow upon exposure to light.

BACKGROUND IF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a novel optical film comprisingone or more polyarylates obtained from the condensation of one or morebifunctional phenolic units having specific substitutions with one ormore bicarboxylic acid. More precisely, the present invention refers toa novel optical film, comprising one or more ortho-disubstitutedbis(hydroxyphenyl)fluorene bisphenol polyarylates, having an excellentstability to ultraviolet and visible light, heat resistance, lighttransparency, high glass transition temperature (Tg) and very goodmechanical properties.

[0003] 2. Background of the Art

[0004] Optical films are well known in the art. Glass has been widelyused for several optical applications, due to its excellentcharacteristics, such as transparency, a high transmittance in thevisible light range and temperature resistance. Notwithstanding thesebenefits, due to its high weight and very high brittleness, the use ofglass as a sublayer or support in optical applications may causeproblems to the final product realization. In addition, because glass isnot flexible, it cannot be used in continuous processing. This leads toa very low final productivity. For these reasons, it indesirable toreplace glass with transparent polymeric films, such as polyesters(e.g., polyethyleneterephthalate), polyacrylates (e.g.,polymethylmethacrylate) or polycarbonate. Even if these polymericmaterials have good handling properties, they have, however, thedisadvantage of poor transmittance, limited heat resistance and a lowglass transition temperature (Tg), whereby the employment of thesepolymers in optical applications has been very limited.

[0005] Polyesters of 9,9-bis-(4-hydroxyphenyl)-fluorene and isophthalicor terephthalic acid are known in the art. U.S. Pat. No. 3,546,165describes such polyesters, which are thermally stable, but generallyhave a relatively low inherent viscosity and unsatisfactory mechanicalproperties. U.S. Pat. No. 4,387,209 describes polyesters made byreacting 9,9-bis-(4-hydroxyphenyl)-fluorene with at least one member ofthe group consisting of isophthalic or terephthatic acid and using aninterfacial polymerization process. The polyester inherent viscositystrongly depends upon the monomer purity, and relatively smallvariations in purity of the diphenol monomer may cause large deviationsin the inherent viscosity values. Example 2 of U.S. Pat. No. 4,401,803describes the preparation of polyesters of9,9-bis-(4-hydroxyphenyl)-fluorene and a 50:50 mixture of isophthalicand terephthalic acid chloride using an interfacial polymerizationprocess. The polyester is precipitated with an acetone-methanol blend toproduce a material with an inherent viscosity of 1.67 dl/g. U.S. Pat.No. 4,533,511 discloses a process for spinning fibers obtained from thepolycondensation product of 9,9-bis-(4-hydroxyphenyl)-fluorene and amixture of isophthalic acid chloride and terephthalic acid chloride.Dichloromethane is suggested as a spinning solvent and the solventprecipitant preferably is an aqueous lower alkanol.

[0006] U.S. Pat. No. 4,066,623 discloses that certain aromatic,halogenated polyesters, prepared by inverted interfacial polymerizationmethods provide a polymer having a low content of low molecular weightfractions which causes a low polymer resistance with respect to thesolvent.

[0007] U.S. Pat. No. 4,967,306 discloses a9,9-bis-(4-hydroxyphenyl)-fluorene/isophthalic and terephthalic acidpolyester which contains a very low level of oligomeric material and hasa tensile strength, elongation, chemical resistance, temperaturestability, ultraviolet resistance and vacuum stability higher than thecopolymers containing oligomeric species described in the art. Filmscontaining small amounts of oligomer will “yellow” or degrade uponlimited exposure to ultraviolet radiation.

[0008] The same polyarylate comprising9,9-bis-(4-hydroxyphenyl)-fluorene and isophthalic and terephthalic acidis also described in JP patent application 57-192432. However, the resincolor tends to the yellow upon exposure to UV radiation due to thediphenol component structure, thus making difficult the use of the resinin optical applications.

[0009] The resin obtained from the polyarylate is composed of9,9-bis-(3-methyl-4-hydroxyphenyl)-fluorene and isophthalic acid asreported in Journal of Applied Polymer Science, Vol. 29, p. 35 to 43(1984). The polymer composed merely of isophthalic acid, results to betoo fragile and has insufficient abrasion resistance and film coatingquality.

[0010] Japanese Patent Application No. 09-071,640 discloses a resincomposed of (a) an aromatic dicarboxylic acid, (b) a specific amount ofa substituted 9,9-bis-(4-hydroxyphenyl)-fluorene and (c) an aliphaticglycol; said resin is utilized in optical materials for its goodtransparency and heat resistance.

[0011] U.S. Pat. No. 4,810,771 discloses polyesters made of mono-orthosubstituted bisphenols, and a blend of isophthalic and terephthalicacid.

[0012] EP Patent Application 943,640 describes a film prepared withpolyarylates synthesized using bisphenolfluorenes mono- andbi-substituted in the ortho position with alkyl (C1-C4) groups. Suchpolyarylates have a better stability to ultraviolet radiation.

[0013] 9,9-bis(3,5-dibromo-4-hydroxyphenyl)-fluorene bisphenol monomerderived polyarylates have been disclosed in PCT Patent Application No.WO 00-33,949 as gas-separation membranes. In U.S. Pat. No. 5,007,945,there is described a polyarylate class obtained from dicarboxylic acidchlorides and cardo bisphenols having halo-substituents on all orthopositions of the phenol groups, which polymer is used to separate one ormore components of a gas mixture. Such patents describe gas-separationmembranes, but do not mention optical films consisting of such polymers.

[0014] The resins, known in the art, obtained from polyarylates composedof 9,9-bis(4-hydroxyphenyl)-fluorene or its ortho mono-substitutedhomologous, even if they have good high temperature resistancecharacteristics and mechanical properties, are subjected to yellowingwhen exposed to light sources and can be therefore hardly used inoptical applications.

SUMMARY OF THE INVENTION

[0015] The present invention refers to an optical film comprising one ormore polyarylates having at least some units represented by the generalstructure:

[0016] wherein A represents one or more different bisphenolfluoreneradicals having the general formula (I):

[0017] wherein R₁ and R₂ independently represent an alkyl group, ahalogen, an alkoxy group, an acyl group, a phenyl group or a nitrilegroup, with the proviso that R₁ and R₂ are not both an alkyl group; R₃,R₄, R₅ and R₆ represent a hydrogen atom, an alkyl group, a halogen, analkoxy group, an acyl group, a phenyl group, a nitro group, or a nitrilegroup;

[0018] B represents one or more different dicarboxy radicals having theformula:

[0019] wherein X is a divalent hydrocarbon group having from 1 to 20carbon atoms, and n is the number of the repeating units which build upthe polymer and is a positive integer higher than 20.

[0020] In the above formulas, as well as in the other formulas describedhereinbelow, the lines terminating without an atom or group indicationrepresent a chemical bond. The optical film of the present invention hasexcellent mechanical and thermal properties, a high Tg and does notreadily yellow upon exposure to light.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention refers to an optical film comprising one ormore polyarylates having at least some repeating units represented bythe general structure:

[0022] wherein A represent one or more divalent radical A, B representone or more divalent radical B and wherein n is the number of therepeating units which build up the polymer and is a positive integerhigher than 20.

[0023] In the above mentioned structure, the radicals A and B arestructurally derived from the relative diphenol and dicarboxylic acid byremoval of a hydrogen atom from the phenolic group and a hydroxy groupfrom the carboxilic group, as if the resulting —A—B— repeating unit wasobtained by a condensation reaction in which a molecule of water (H₂O)was removed. Although the mechanism of this reaction is not critical,and it may be possible for other reactions or reaction mechanisms toprovide the same structure for the product (for example, by removal of amolecule of HCI from a phenol and a carboxylic acid choride), thatproduct and the individual resultant groups shall be referred to in thepractice of the present invention (solely for the purposes ofconvenience and not for limiting the mechanism of formation) to acondensation product, condensation-like product, condensation derivativeor condensation-like derivative.

[0024] The wording “one or more radical A” or “one or more radical B”means that the optical film of the present invention can contain apolyarylate deriving from the condensation of one or more radical A withone or more radical B so that the resulting polymeric structure cancomprise a random structure of several different radicals A with severaldifferent radicals B, such as, for example, —A—B—A′—B′—A—B′—A′—B′.

[0025] In the above described repeating unit, radical A represents oneor more different bisphenolfluorene radicals having the general formula(I):

[0026] wherein R₁ and R₂ independently represent an alkyl group, ahalogen, an alkoxy group, an acyl group, a phenyl group or a nitrilegroup, with the proviso that R₁ and R₂ are not both an alkyl group; R₃,R₄, R₅ and R₆ represent a hydrogen atom, an alkyl group, a halogen, analkoxy group, an acyl group, a phenyl group, a nitro group, or a nitrilegroup.

[0027] In the above reported formula, R₁ and R₂ preferably represent alinear or branched alkyl group having form 1 to 6 carbon atoms, such ase.g., methyl, ethyl, butyl, isopropyl; a halogen atom, such as chlorine,bromine, iodine or fluorine; a linear or branched alkoxy group havingfrom 1 to 6 carbon atoms, such as e.g., methoxyl, ethoxyl, butoxyl; anacyl group having from 1 to 20 carbon atoms, such as e.g., acetyl,propionyl; a phenyl group or a nitrile group, with the proviso that R₁and R₂ are not both an alkyl group; and R₃, R₄, R₅ and R₆ preferablyrepresent a hydrogen atom, a linear or branched alkyl group, preferablyhaving from 1 to 6 carbon atoms (such as e.g., methyl, ethyl, butyl,isopropyl); a halogen atom (such as chlorine, bromine, iodine orfluorine); a linear or branched alkoxy group, having from 1 to 6 carbonatoms (such as e.g., methoxyl, ethoxyl, butoxyl); an acyl group havingfrom 1 to 20 carbon atoms (such as e.g. acetyl, propionyl, etc.); aphenyl group or a nitrite group.

[0028] Preferably, radical A represents one or more different or similarbisphenolfluorene radicals having general formula (II):

[0029] wherein R₁ and R₂ (as described above) represent a linear orbranched alkyl group having from 1 to 6 carbon atoms, such as e.g. amethyl, ethyl, butyl group, a halogen atom, such as chlorine, bromine,iodine or fluorine, with the proviso that R₁ and R₂ are not both analkyl group.

[0030] In the above described repeating unit, radical B represents oneor more different decarboxy radicals having the formula:

[0031] wherein X is a divalent hydrocarbon group having from 1 to 20carbon atoms, such as, for example, a saturated or unsaturated aliphaticgroup (e.g., methylene group, ethylene group, propylene group, butylenegroup) or an aromatic group (such as a phenylene group, naphthalenegroup or diphenylene group).

[0032] In the above reported formula, X is preferably a divalentaromatic group having from 6 to 20 carbon atoms, such as arylene groups,naftylene groups and difenylene groups represented by the followingformulas:

[0033] More preferably, the optical film of the present inventioncomprises one or more polyarylates comprising one or more differentrepeating units represented by general formula (III):

[0034] wherein R₁ and R₂ are as defined in formula (II) and n is apositive integer higher than 20. Still more preferably, the presentinvention refers to an optical film comprising one or more polyarylatescomprising two different repeating units represented by9,9-bis-(4-hydroxyphenyl)-fluorene radicals of general formula (II)linked with two dicarboxy radicals derived from two differentdicarboxylic acids, such as isophthalic acid and terephthalic acid,1,2-dinaphthoic acid and 1,4-dinaphthoic acid,1,1′-diphenyl-4,4′-dicarboxylic acid and 1,1′-diphenyl-4,2′-dicarboxylicacid, isophthalic acid and 1,2-dinaphthoic acid, and the like. Thedicarboxylic acids are usually mixed in a weight ratio of from 1:10 to10:1, preferably from 1:4 to 4:1. Most preferably, isophthalic acid (ora derivative thereof) and terephthalic acid (or a derivative thereof) ina weight ratio of from 1:4 to 4:1 are used.

[0035] When in the present invention the term “group” is used todescribe a chemical compound or substituent, the described chemicalmaterial comprises the group, ring and base residue and that group, ringor residue with conventional substituents. When on the contrary the term“unit” is used, the unsubstituted chemical material is intended to beincluded. For instance, the term “alkyl group” comprises not only thosealkyl units, such as methyl, ethyl, butyl, octyl, etc., but also thoseunits bearing substituents such as halogen, nitrite, hydroxy, nitro,amino, carboxy, etc. The term “alkyl unit” on the contrary comprisesonly methyl, ethyl, cyclohexyl, etc.

[0036] Polyarylates useful to the present invention comprise thefollowing repeating units (wherein n is the number of repeating unit andis an integer higher than 20), even if the present invention is notlimited thereto.

[0037] The bisphenolfluorene monomers described in the present inventionhave been obtained with methods known in the art, such as for instancewith the method described in U.S. Pat. No. 5,248,838.

[0038] The polyarylates used in the present invention can be preparedwith methods known in the art: there can be used for instance thesolution polymerization method described in Ind. Eng. Chem. 51, 147,1959, wherein a bifunctional carboxylic acid dihalide reacts with abifunctional phenol in an organic solution; the “molten” polymerizationmethod, wherein a bifunctional carboxylic acid and a bifunctional phenolare heated in the presence of acetic anhydride or diallylcarbonate, asdescribed in JP patent application 38-26299; or the interfacialpolymerization method, wherein a bifunctional carboxylic acid dihalidedissolved in a hydrophobic organic solvent is mixed with a bifunctionalphenol dissolved in alkali water solution, as described in J. PolymerScience, XL399, 1959 and in EP patent applications 943,640 and 396,418.

[0039] The optical films of the present invention can be obtained withmethods known in the art, such as for instance with the solvent coatingtechnique which consists of preparing a polymer solution, herein definedas collodion, in an organic solvent and pouring this solution onto abase, such as metal, glass or plastic material; the film is thenobtained after drying the collodion and subsequent release from thebase. Generally, organic solvents are used, such as e.g., halogenatedsolvents (such as methylene chloride, chloroform, tetrachloroethane,dichloroethane, etc.) or other solvents such as N-methylpyrrolidone,N,N-dimethylformamide, dioxane, tetrahydro-furane, etc.

[0040] Other methods known in the art than can be used to obtain thefilms of the present invention are the one known as “spin coating”,wherein the collodion is poured onto a quick-rotating base, or the hotextrusion or hot lamination methods, which are based on a molten polymerprocessing.

[0041] The thickness of the optical film of the present invention rangesfrom 0.1 to 1000 μm, preferably from 1 to 1000 μm.

[0042] The optical film of the present invention shall be highlytransparent and have the slightest possible amount of impurities orsurface or inside defects such as not to cause interference with thelight radiation passing through it. To obtain such properties, it isadvisable to filter the collodion with techniques known in the art, byusing filters with pores having sizes of less than 10 μm, preferablyless than 1 μm, more preferably less than 0.1 μm.

[0043] The optical film object of the present invention may haveadditional protective layers on one or both surfaces in order to improvesome of its characteristics, such as for example solvent resistance, gasand water vapor permeability, mechanical properties, surface scratchresistance, light radiation resistance. The protective layers mayconsist of organic or inorganic materials or mixtures thereof and can beapplied with techniques known in the art, such as for instance thesolvent coating technique (described in U.S. Pat. Nos. 4,172,065;4,405,550; 4,664,859 and 5,063,138), the vacuum coating technique(described e.g. in U.S. Pat. Nos. 4,380,212; 4,449,478; 4,485,759 and4,817,559), the lamination technique (described e.g. in U.S. Pat. Nos.4,844,764; 5,000,809; 5,208,068 and 5,238,746) or resin reticulationwith an electron beam or an ultraviolet radiation, as described e.g. inWO application 96-24,929 and JP 02-260145.

[0044] The optical film of the present invention, at the inside or inadditional layers thereof, may contain ultraviolet radiationstabilizers, such as for instance benzophenone compounds (e.g.,hydroxy-dodecyloxy benzophenones, 2,4-dihydroxybenzophenones, and thelike), triazole compounds (e.g.,2-phenyl-4-(2′,2′-dihydroxybenzoyl)-triazole, substitutedhydroxy-phenyltriazoles, and the like), triazine compounds (e.g.,hydroxyphenyl-1,3,5-triazine, 3,5-dialkyl-4-hydroxy-phenyl-triazine, andthe like), benzoate compounds (e.g., diphenolpropane dibenzoate,diphenolpropane tert.-butyl-benzoate, and the like), sterically hinderedamine and other compounds like those described for instance in U.S. Pat.Nos. 4,061,616 and 5,00,809.

[0045] The optical film of the present invention, in the inside oradditional layers thereof, may also contain transparent pigments toimprove the film durability, such as for instance metal oxides (e.g.,titanium dioxide, zinc oxide, iron oxide), metal hydroxides, chromates,carbonates, and the like, such as those described for instance in U.S.Pat. No. 5,000,809. In addition, the optical film of the presentinvention may also contain slip agents (such as the wetting agentsdescribed in JP patent application 02-260,145) and antioxidizing andstabilizing substances, such as, for example, sterically hindered phenolantioxidizers, organic and inorganic phosphites,ortho-hydroxybenzotriazoles or antistatic agents to decrease staticcharge storage and the consequent attraction of powder onto the opticalfilm.

[0046] The optical films of the present invention can be widely used inthe optical application field, such as for instance in panels orflattened layers for liquid crystal screens, in supports and protectivelayers for electroluminescent screens, in polarizer transparentconducting films, and similar applications due to their good mechanicalproperties, such as tensile strength, dimensional stability, further tobeing completely amorphous and transparent and having a high heatresistance and a high Tg. Their use as lens, both ophthalmic lenses,planographic lenses, and focal lenses is also contemplated in thepractice of the invention.

[0047] The present invention is now illustrated by reference to thefollowing examples which however are not construed as limiting it.

EXAMPLES Example 1

[0048] Comparison film 1 was obtained by taking compound A andpolymerizing it with the interfacial polycondensation technique asdescribed in EP patent 396,418, utilizing a 1:1 mixture of ofterephthalic and isophthalic acids. The so-obtained polymer was coatedwith the solvent coating technique using a 10% weight methylene chloridesolution of the polymer. The film was then dried for 3 hours at atemperature of 25° C., gradually increasing the temperature up to amaximum of 160° C.

[0049] Comparison film 2 was obtained with the same procedure, but usingcompound B instead of compound A.

[0050] Film 3 (invention) was obtained with the same procedure, butusing polymer 4 of the present invention instead of the polymer obtainedfrom compound A.

[0051] Film 4 (invention) was obtained with the same procedure, butusing polymer 2 of the present invention instead of the polymer obtainedfrom compound A.

[0052] Film 5 (invention) was obtained with the same procedure, butusing polymer 3 of the present invention instead of the polymer obtainedfrom compound A.

[0053] Films 1 to 5 were then exposed to a light source using anOriginal Hanau Xenotest 150 photostability test equipment, equipped witha 1500 W Xenon lamp delivering about 180,000 lux continuousillumination. The absorbance in the range from 320 and 500 nm was thenmeasured before and after the exposure of 50 hours to the said lightsource. Tables 1a and 1b show the absorbance values of the five filmsmeasured before and after the 50 hours exposure, respectively. TABLE 1aFresh Film Wavelength Film 1 Film 2 Film 3 Film 4 Film 5 (nm) (ref.)(comp.) (inv.) (inv.) (inv.) 320 5.00 3.24 1.76 1.47 1.73 330 4.48 1.300.46 0.53 0.42 340 2.00 0.52 0.19 0.24 0.18 350 0.72 0.22 0.11 0.13 0.10360 0.27 0.11 0.09 0.10 0.09 370 0.13 0.09 0.08 0.09 0.08 380 0.09 0.080.07 0.08 0.07 390 0.08 0.07 0.07 0.08 0.07 400 0.07 0.07 0.07 0.06 0.06500 0.06 0.06 0.06 0.05 0.05

[0054] TABLE 1b Aged Film Wavelength Film 1 Film 2 Film 3 Film 4 Film 5(nm) (ref.) (comp.) (inv.) (inv.) (inv.) 320 5.00 3.32 2.46 2.25 2.79330 4.79 2.04 0.95 1.28 1.30 340 3.74 1.03 0.58 0.68 0.81 350 3.37 0.610.42 0.45 0.55 360 2.62 0.40 0.33 0.35 0.39 370 2.29 0.30 0.27 0.28 0.31380 1.76 0.22 0.22 0.23 0.23 390 1.22 0.18 0.17 0.18 0.20 400 0.78 0.150.15 0.14 0.16 500 0.07 0.07 0.07 0.06 0.06

[0055] The data reported in Table 1 show that comparison film 1,obtained with a bisphenolfluorene polyarylate not substituted in thebisphenol ortho positions, dramatically increases the absorbance valuesmeasured at 400 nm, the blue light absorption range, with theconsequence of an undesired strong yellow coloration. On the contrary,films 2 (comparison) and 3 to 5 (of the present invention), obtained bypolymerizing bisphenolfluorenes bearing substituents in the orthopositions thereof, have a very little increase of the absorbance valuemeasured in the range of 400 nm after a 50 hour exposure, with respectto the value of the virgin film.

Example 2

[0056] Films 2 to 5 were cut into 70 mm long and 15 mm wide stripes andintroduced into an Instron 5564 dynamometer working with a 50 mm jawspacing. Table 2 shows the resulting values of tensile strength(expressed in MegaPascal) and Young modulus (expressed in GigaPascal).TABLE 2 Mechanical Tensile strength Young modulus properties (MPa) (Gpa)Film 1 90 2.5 (Comparison) Film 2 78 2.8 (Comparison) Film 3 120 3.4(Invention) Film 4 100 2.8 (Invention) Film 5 133 3.2 (Invention)

[0057] Table 2 shows that the comparison film 2, obtained from apolyarylate consisting of a bisphenolfluorene in all ortho positionsthereof substituted only with methyl groups, has a particularly lowtensile strength with respect to films 3 to 5 of the invention, obtainedby polymerizing bisphenolfluorenes having at least one ortho-substituentother than methyl group. The tensile strength of comparison film 2 iseven lower than that of comparison film 1. Such a low tensile strengthgives the film 2 worse mechanical properties, thus making it morefragile and therefore more sensitive to breaking caused by mechanicalstresses during the film processing and converting. Young modulus isalso improved when using films 3 to 5 of the invention.

Example 3

[0058] Films 2 to 5 were thermally characterized by means of a) aPerkin-Elmer DSC-4 Differential Scanning Calorimeter, by following aheating ramp of 10° C./min. starting from a temperature of 50° C. up to400° C. under a continuous nitrogen stream, determining the glasstransition temperature value (Tg) and b) a thermogravimetric analysis bymeans of a Perkin Elmer TGS-2 Thermogravimetric Analyser/MicrobalanceModel AR-2, following a heating ramp of 10° C./min starting from atemperature of 50° C. up to 800° C., determining the decompositiontemperatures under air and nitrogen flow. Table 3 reports the values ofsuch thermal properties expressed in ° C. TABLE 3 Thermal Film 2 Film 3Film 4 Film 5 properties (comparison) (invention) (invention)(invention) Glass transition 334 342 346 365 temperature (Tg) Air decom-350 385 387 408 position temperature Nitrogen 357 394 392 408decomposition temperature

[0059] Table 3 shows that comparison film 2, obtained from a polyarylateconsisting of bisphenolfluorene in all ortho positions thereofsubstituted only with methyl groups, has a glass transition temperature(Tg) lower than that of films 3 to 5 of the present invention, whichwere obtained on the contrary with compounds not having only methylgroups as substituents in the bisphenolfluorene ortho positions.

[0060] Moreover, comparison film 2 exhibits both air and nitrogendecomposition temperature values definitely lower than those of films 3to 5 of the present invention. The decrease in the decompositiontemperature of film 2, which is too close to the glass transitiontemperature, makes it difficult to use the film at temperatures near Tg,whereto many processings are performed (such as stretching, extrusion,lamination). The wide interval between decomposition temperature and Tgin films 3 to 5 of the present invention allows them to be used attemperatures near or even higher than their Tg without thereby causingdecomposition phenomena.

Optical Film Comprising Polyarylates Containingbis-(hydroxyphenyl)-fluorene-ortho-disubstituted Bisphenols

1. An optical film comprising one or more polyarylates comprisingrepeating units represented by the general structure:

wherein A represents one or more different bisphenolfluorene radicalshaving the general formula (I):

wherein R₁ and R₂ independently represent an alkyl group, a halogenatom, an alkoxy group, an acyl group, a phenyl group or a nitrite group,with the proviso that R₁ and R₂ are not both an alkyl group; R₃, R₄, R₅and R₆ represent a hydrogen atom, an alkyl group, a halogen, an alkoxygroup, an acyl group, a phenyl group, a nitro group, or a nitrile group;B represents one or more different dicarboxy radicals having theformula:

wherein X is a divalent hydrocarbon group having from 1 to 20 carbonatoms, and n is the number of the repeating units which build up thepolymer and is a positive integer higher than
 20. 2. The optical film ofclaim 1, wherein said bisphenolfluorene radical A is represented by theformula:

wherein R₁ and R₂ represent an alkyl group or a halogen with the provisothat R₁ and R₂ are not both an alkyl group; and said dicarboxy radical Bis represented by the formula:

wherein X is a 6 to 20 carbon atom divalent hydrocarbon group.
 3. Theoptical film of claim 1, wherein said divalent hydrocarbon group X isselected from the group consisting of:


4. The optical film of claim 1, wherein said one or more polyarylatesare represented by the formula:

wherein R₁ and R₂ represent an alkyl group, a halogen atom, an alkoxygroup, an acyl group, a phenyl group or a nitrite group, with theproviso that R₁ and R₂ are not both an alkyl group; and n is a positiveinteger higher than
 20. 5. The optical film of claim 4, wherein said oneor more polyarylates comprise a at least a first dicarboxy radical and asecond dicarboxy radical, the weight ratio between said first dicarboxyradical and said second dicarboxy radical being of from 1:10 to 10:1. 6.The optical film of claim 5, wherein said first dicarboxy radical isderiving from isophthalic acid and said second dicarboxy radical isderiving from terephthalic acid.
 7. The optical film of claim 6, whereinthe weight ratio between said first and second dicarboxy radicals is offrom 1:4 to 4:1.
 8. The optical film of claim 1, wherein said one ormore polyarylates are selected from the group consisting of:

wherein n is the number of repeating units and is an integer higher than20.